How to remove array duplicates in JavaScript

The Set collection#

Since ES6, Set collection has been introduced which is really good and makes our life simple. Set is a collection which will not keep duplicates. It can also take any iterable objects as constructor arguments. In our case, it is an array with duplicated values.

const duplicates = [1, 2, 3, 3, 2, 1]

const unique = [...new Set(duplicates)]

console.log(unique) // [ 1, 2, 3 ]

Array.filter function#

It is better to know more options, in case of not-so-friendly environment. For instance, Set collection is supported by all the major browsers but few old-schools. Yes, I am looking at you IE! O_o

const duplicates = [1, 2, 3, 3, 2, 1];

const unique = duplicates.filter(
(item, index) => duplicates.indexOf(item) === index
);

console.log(unique); // [ 1, 2, 3 ]

Please prefer the Set option just for the simple of it!

We can do the same .indexOf trick using .map, .foreach as well. But, .filter is more readable among those! ^_^